AE Buttons Plus! Lets you remap your volume keys, center dpad button, etc... (back and home keys cannot be remapped with this program though). The keys you can remap, you can assign them with activating actions with one press, two press, three press, and long holds... so you get more out of each key. Hope this helps.
here you go for more info:
http://forum.ppcgeeks.com/showthread...=hardware+keys
edit: i remapped the center button for a long hold to act as the ok/close button
the back button does work to close things, but in certain programs like opera it doesn't work like that....